This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Amyloid fibers are formed when normally soluble proteins change conformation to form insoluble filaments that can cause severe damage and even death. Amyloidoses include Alzheimers disease type II diabetes hereditary amyloidoses and a variety of prion diseases including Creutzfeldt-Jakob disease BSE (mad cow disease) and scrapie. Mammalian prions are infectious protein aggregates formed by the protein PrP when it folds into aberrant structures. Amyloids are also formed by yeast prion proteins. Amyloid proteins share a cross-beta structure but the structural details are not known. Amyloid fibers cannot be characterized by crystallography or NMR. Fiber diffraction is an effective method for determining the structural details of filamentous assemblies and offers the best hope for elucidating the structures of prions and other amyloids. Structural studies are needed to answer fundamental protein folding questions to understand amyloid formation and for rational drug design. We use very small quantities of material to make dried fibers under controlled conditions. Recombinant prions open up new possibilities of obtaining material but we have shown that there are structural differences between synthetic and brain-derived prions which have yet to be characterized fully. Improved prion availability improved methods of specimen preparation and intense high quality synchrotron radiation together offer an unprecedented opportunity to obtain improved amyloid diffraction data. Data will be obtained from synthetic amyloid peptides from mammalian scrapie-derived prions and from recombinant scrapie-derived prions. Wide-angle and low-angle data will be collected. We have shown that meridional data can determine the nature of the cross-beta structure and equatorial data can be used to describe protofilament structure. The complete diffraction data will be used to evaluate and improve competing models for amyloid structure.